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What is the thrust balance between compressor and exhaust nozzle for a turbojet engine?
I had this question asked in university and the teacher was unable to provide more than a theoretical estimate. The ratio I was given was 15/85.
Obviously in the case of a turbofan this ratio increases.
Is there any professional pilot or engineer able to tell even on a real example, what is the ratio of thrust distribution between compressor and jet for a known reactive jet engine, turboprop or turbofan?
I believe that helicopter turboprops produce no measurable thrust in the jet. Anyone?

What do you mean developed by suction? Do you mean the force applied to the compressor (basically all of it, actually; there is otherwise more forward-facing than aft-facing surfaces, so the force on the compressor is more than the total thrust), the force due to decrease of pressure ahead of the compressor as opposed to increase behind it (there is overpressure ahead of it once the aircraft gains ~M0.5, the “pressure recovery”, and it is important part of the reason jet engines remain efficient to high speeds)…?

The compressor acts as a tubed multi blade propeller. It compresses the airflow and the reactive effect is thrust on each rotor blade. What is the ratio between the thrust developed in compressor and the thrust developed in the exhaust nozzle?

For engines with subsonic exhaust, which is what most airliners use, the nozzle is purely convergent, so it does not have any aft-facing surface on which positive thrust could be generated. The compressor is the only major aft-facing surface, so the forward force on it is most of thrust, plus force to compensate the backward force on the turbine and the convergent part of the nozzle. It wouldn't be producing nearly as much thrust without the nozzle though, and it would not produce any without the combustor and turbine.

Are you looking for a breakdown of the forces on each section, like in the answers here? On which point(s) in a jet engine does the reaction force act?

The answer depends on two major factors: the engine design, and the flight speed.

Engine design. As mentioned in this answer, there are four major types of turbine engine design: turbojet, turbofan, turboprop, turboshaft. The turbojet has all air flow through the engine itself and derives all thrust from the combustion gas jet exhaust. At the other end of the spectrum, the turboshaft has negligible thrust from the hot exhaust and transfers all useable power to the output shaft.

Flight speed. At high speed (case a in above picture) air streams into the inlet at high velocity and is decelerated before it hits the compressor, which sees a static pressure at the front that is higher than ambient pressure. No suction at the compressor front end at high speed! Only at the lower speed of case b is the static pressure at the front of the compressor lower than ambient.

To start with the last question:

I believe that helicopter turboprops produce no measurable thrust in the jet. Anyone?

Helicopter engines are turboshafts, which transfer all useful power onto the output shaft. No thrust from the exhaust stream here, ratio 100/0
Then the title question, which is a bit confusing because of the use of the word suction. IF we take the question as posted in a comment, it seems to focus on turbofans, and on the thrust ratio between hot stream and cold stream:

The compressor acts as a tubed multi blade propeller. It compresses the airflow and the reactive effect is thrust on each rotor blade. What is the ratio between the thrust developed in compressor and the thrust developed in the exhaust nozzle?

Two sources for the answer:

From The Jet Engine 5th edition by Rolls Royce, page 94:

A compressor is a device that raises the pressure of the working fluid passing through it - in this case, air. A fan is a large, low-pressure, compressor found at the front of most modern aero engines.

For a modern large civil engine:the fan passes over one tonne of airflow per second; this flow produces around 75 per cent of the engine thrust

Gas Turbine Theory by Saravanamuttoo a.o. example 3.2, finds a ratio of 73.5% at sea level:

   Thrust of a twin-spool bypass engine with the following data:
   * Overall pressure ratio           25.0
   * Fan pressure ratio                1.65
   * Bypass ratio                      5.0
   * Total air mass flow             215 kg/s
   * Fan thrust (cold stream)     52,532 N
   * Exhaust thrust (hot stream)  18,931 N

These above percentages are from the engine itself - but in cruise flight, a large part of thrust is developed by different structural parts of the engine, notably the engine intake.

A supersonic turbojet engine with central intake cone, from TUDelft lecture handout D-32A Propulsion of Aircraft by Prof. Wittenberg. The inlet starts developing thrust at below M = 1. A subsonic engine has its inlet optimised for lower velocities, which will the contribute more to the thrust in cruise.
Please note that the above picture contains a graph for Inlet Thrust, not for compressor thrust. The compressor is an internal part of the engine, thrust is only delivered from external interaction between atmosphere and engine - in the inlet and the exhaust.

Thank you for the answer. I understand pretty much of it. With some parts I’m not comfortable as to agree. I’ll be very brief: the four jet categories are not what I’ve learned so far. Turbo shaft is the driver and turboprop is the assembly turbo shaft plus propeller assembly. Turbofan is derived from turbojet. But these are minor differences and I guess different sources could lead to variations. You have focused on turbofan, I thank you for that. I would really appreciate if you- or anyone could provide any relevant data for a turbojet engine.

All thrust of a turbojet is delivered via the hot stream exhaust. I cannot make sense of your question when related to a turbojet, do you mean what portion of power does the compressor absorb?

The thrust developed in the turbojet is split between thrust developed in the axial compressor and the thrust developed in the exhaust nozzle. The axial compressor develops thrust because is a tubed propeller. No turbojet develops thrust in the exhaust nozzle alone. It is possible for the ramjet to develop thrust in exhaust nozzle alone, but that is a different engine flying in supersonic mode only. I am interested to find what is the balance of thrust between compressor and exhaust nozzle in a turbojet.

The compressor in a turbojet develops rear facing force all right, but it is an internal force. It pushes back onto the rest of the engine aft of it, like a person sitting in a sailboat and directing a fan at the sail.: no net thrust. Internal compression develops no thrust, only compression released into the environment does. The net gain in exhaust energy comes from the fuel combustion, behind the compressor.

The compressor does not develop rear facing force. It develops a forward force because each  compressor blade forces the air through and in exchange the blade is forced forward, pulling the entire compressor forward. A person operating a fan on a boat induces thrust because the fan moves the air which in turn acts on each fan blade. The net gain in energy... what exactly are you contending in your answer already syndicated by the upvoting machine?


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How can luggage be lost if it has a bag tag?
I lost a bag on a flight from BKK -> ARN -> CPH two weeks ago. I immediately filed a report at CPH when the bag hadn't arrived after more than an hour of waiting. Since then there has been no updates of the bags whereabouts on the tracing website.
As a layman, the only reasonable explanation for the bag being missing for more than a few days seems to be that the luggage tag has somehow fallen off the bag. If the luggage still has a tag and is sitting somewhere in an airport - be it at BKK, ARN or CPH - surely someone would have noticed it by now and scanned the tag?
However, when reading about why luggage gets lost, and especially seeing photos of lost luggage at auctions, it seems that it's entirely possible for a bag to still have its tag with barcodes intact and yet be "missing".
How can this be? Surely the system must be built in such a way that a luggage handler can scan the bag tag at any time and either find the missing luggage report or the contact details of the passenger? Or is the luggage handling identification system a lot dumber than I imagine? I read somewhere that "after 3 days the barcode is reused for other passengers luggage", which sounds too stupid to be true.
It would be interesting to know how it works, perhaps someone here can shed a light?

To the downvoter: Please explain why you voted, especially to a new user! @Magnus, I think this question is only borderline related to aviation and might be a better fit for travel.stackexchange, where all passenger related questions should go.

Just a thought, but i think a question like this is waaaay more likely to reach someone who can answer it here than on travel SE...

Hmm yeah I'm thinking that the people on the Travel StackExchange are mostly travellers whose guesses are as good as mine. I'm hoping someone here actually has insight into the baggage handling systems and how they work in real life (which might differ from the descriptions in the biased industry websites, where it sounds all fine and dandy and impossible that luggage would ever get lost for more than a few days at most...)

To the moderators who say that the question is off topic - it's clearly about ground operations, airport-operations and baggage-handling-systems, exactly as tagged with tags that exist on Aviation StackExchange and not on Travel StackExchange.

Perhaps for the same reason that I sometimes get mail or packages that are addressed to my neighbors.  People and machines make errors.  Nevertheless, this has nothing whatsoever to do with aviation, so downvoted.

@jamesqf The obvious difference is that in those cases the freight company will most likely be able to track the package up until the last time it was scanned. If it is routed incorrectly that will all appear in the log, and it will be resorted and rerouted to the correct receiver. If you know, please tell me how it works in the case of airline luggage. If you don't know, then let someone who does answer the question.

@Magnus W: If you want a technical answer, ask the question in an appropriate place.  Baggage or package handling has nothing to do with aviation, so it's pretty unlikely that you'll get a better answer here.  Even for commercial pilots, it's just stuff that goes in the hold :-)

@MagnusW could you raise the issue on meta? I think it is best to discuss the situation there

@jamesqf this site isn't just for pilots!

@Notts90: Perhaps it should be?  Not just pilots, of course, but anyone interested in what's involved in actual flying.  This question obviously doesn't have ANYTHING to do with flying.  The same problems would arise in ANY parcel-handling system, whether it's the post office, Amazon's shipping department, container ships...

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Airfoil and Wing Analysis for Transonic Speed (M = 0.85 and Re = 42 million)
I am working on a project where I have to design a plane which has to cruise at 0.85 Mach at 35,000 ft. While working on the wing design, I quickly discovered that 6 series airfoils, with a good amount of thickness ratio, have a low Critical Mach Number. So, I started exploring Supercritical Airfoils (SC Airfoils). F or doing analysis of SC airfoils can XFLR5 be used?
Moreover, Aspect Ratio and Sweep also influence Critical Mach Number.
Is there are a relationship that connects these three entities?
Lastly: is there a credible source that compiles the analysis of Transonic Airfoils (Supercritical Airfoil)?  (Similar to Theory of Wing Sections by Abbott and Doenhoff, which contains data for conventional airfoils)

Can I suggest you take the site tour? You have a bunch of questions posted as one, which runs counter to the format. Could you edit this down to a single question?

@AEheresupportsMonica Thanks for providing guidelines for improving the question !

@KorvinStarmast Thanks for further more reframing the question !

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What's the benefit of cranked wing for commercial airplanes
Many commercial airplanes have a kink in the wing geometry.

A discontinuous change in the wing trailing edge sweep is present in the wing of the A320. What's the benefit of this? Is there any aerodynamic advantage?

Oops! Thanks for pointing it out.

It may be very useful to study the Handley Page Victor.  Many of today's issues, such as tail requirement, critical Mach number, placement of jet engines, and drag reduction were addressed with this ungainly, but very practical aircraft.  They "repeatedly refueled" the delta Vulcans on long range missions.

@RobertDiGiovanni Thanks for the reference! I will surely look into it.


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During which phase of the mission profile, the airplane fastest?
In a mission profile, there are various phases such as Climb, Cruise, and Descent (excluding other phases). My question is during which of these phases, the Mach number of the airplane is highest? Is that Mach number more or less than critical Mach Number?

It seems you have 2 different questions (the flight phase and the critical mach number). Those two questions are independent enough to be asked in 2 different questions. You may thus consider splitting your question in 2 different posts

Mach number is likely to be highest when the aircraft is highest.
Mach number is related to true air speed (TAS) while the power required is related to the indicated air speed (IAS). As a plane flies higher, the air becomes thinner. Typically a plane will fly at a constant IAS, so the aerodynamic forces remain constant, but the TAS (and ground speed, and Mach number) increase.
As a plane burns fuel and gets lighter, it can fly higher, so just before the descent could be the highest Mach number.

This isn't really true for jet aircraft, which typically cruise at a fixed Mach number.


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Design lift coefficient of an airfoil
I have the design lift coefficient of the plane during the cruise condition. Now, I want to calculate the lift coefficient required by the airfoil which makes up the wing, taking into account the Aspect Ratio, Sweep, etc. Is there a formula for that? I have seen formulas that give the slope of the lift curve for a wing using the slope of the lift curve of an airfoil.
I need the design lift coefficient of the airfoil for choosing an appropriate airfoil.

Okay, that can be done. I had one more doubt. At each span location, will the lift coefficient (of the airfoil at that location) be different or will it be the same? As we move in the spanwise direction, the lift will decrease and the chord also decreases. Therefore, can we say that lift coefficient will be same cross the span?

Oh, I see. I forgot about the downwash and spanwise flow. Then how can one chose an airfoil if one has design lift coefficient of the wing?

Then, I will add another question.

As far as your question on sectional lift given a wing geometry and total lift coefficient is concerned, there is no one single formula that estimates this. The sectional lift is affected by downwash and spanwise flow, which are in turn dictated by the wing geometry and airfoil themselves.
For straight tapered wing, you can use the lifting-line, which computes the downwash angle at the discrete spanwise locations, which you can use to easily back-out local $C_l$. For swept wing, your easiest solution is to use a vortex-lattice method, such as AVL. AVL directly outputs the section lift coefficient at the corresponding control points.
As far as selecting/designing an airfoil is concerned, it's much more involved than just looking at the cruise lift coefficient. You should consider:

Takeoff and landing requirements. What kind of performance do you need? What kind of trailing-edge and/or leading-edge devices can you fit with the airfoil?
Operating conditions. Is it a point-design? Or does it need to cater for large range of operating conditions?
Structural concerns. Can you actually manufacture a super thin trailing-edge, even if it gives the best stall characteristics? Can you actually fit a spar tall enough (and at the right location), even if it gives the best drag characteristics?
Space concerns. Can you actually fit fuel tanks in the wing if it's super thin?


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How many significant digits should I use for simulating aircraft equations of motion?
I have coded the equations of motion in Matlab, and I am using the ode45 function to simulate the nonlinear dynamics of F/A-18 Hornet without any controller (just the airframe). I have given initial conditions as trim conditions.
d2r = pi/180;           % degree to rad

V       =  438.653328;  % Airspeed , ft/s
beta    =  0*d2r;       % Sideslip Angle, rad
alpha   =  10*d2r;      % Angle-of-attack, rad

p       =  0*d2r;       % Roll rate, rad/s
q       =  0*d2r;       % Pitch rate, rad/s
r       =  0*d2r;       % Yaw rate, rad/s

phi     =  0*d2r;       % Roll Angle, rad
theta   =  10*d2r;      % Pitch Angle, rad
psi     =  0*d2r;       % Yaw Angle, rad

pN = 0;                 % X position in Earth Frame, ft
pE = 0;                 % Y position in Earth Frame, ft
h = -25000;             % Z position in Earth Frame, ft

During the first iteration, C_m has a very positive small value (1e-10), which leads to some pitching moment when multiplied by S, c, and qbar (even though it's small). But, as time keeps on increasing, this value of C_m goes on increasing and as a result, a large moment is created. Due to the high precision of Matlab, the pitching moment coefficient is not for the given trim condition.
My question is: should I round off the values of C_m to 3 or 4 digits? By rounding off, the C_m will be zero and I get M as zero.
The below figure shows how velocity is varying with time when the aforementioned initial conditions are given.
This figure is obtained after rounding off C_m to 4 significant digits.

This figure is obtained without rounding off C_m to 4 significant digits.

Alpha and theta values without rounding off C_m.

Wait, why does C_m (pitching moment coefficient of the whole aircraft) increase? What is the value (or at least sign) of its main component, the $C_m^{\alpha}$ (or $^{n_z}$) derivative? It should determine pitch stability, given that the rest is basically damping. If it's pitch stable (the derivative is negative), the computational errors should not be significant.

The sign of the pitching moment is positive, which shows that it is unstable. So, without external control, it will not be in equilibrium (irrespective of trim condition input), right?

It looks to me as if the simulation rate is too low. The rounding of the numbers could create better results just because it happens to better align with the simulation rate. (I think it's called aliasing effect)

Positive pitching moment simply means nose up. What determines stability is its derivatie (by angle of attack or normal acceleration), which is a parameter of the model itself. (It is, of course, a function of other parameters such as CG location). If the derivative is positive, the model/aircraft is unstable, and it doesn't matter much which kind of disturbance you induce. If you cheat with C_m, you will see instability the moment you start changing other things (e.g. normal fligtht control).

In fact, judging by the last graph you added (I understand it's airspeed - but pitch or alpha would be more indicative), the model is stable. It's just the initial trim condition is a bit off, and it accumulates over time, which results in a typical phugoid motin. By reducing precision, you are forcing it to be 'on' trim. Basically, it looks like there is nothing wrong with the model as it is. If you add control, you should be able to fly it.

I have added the plot for alpha and theta.

@Pavan You shouldn't truncate anything artificially. Is it possible that it's just a bad trim point? From your new plots, it looks like the model is trying to stabilize somewhere else.

@JZYL, I will surely look into it.

From your description, it's not an issue with the aerodynamic coefficients. If as you have described previously that you're modeling F-18, then the airframe should be unstable longitudinally. A 1e-10 deviation (assuming it applies to body rates, body speeds, etc. as well) is well-within typical trim error bound; in fact, a deviation is unavoidable when dealing with computational floating point. But if it's longitudinally unstable, any deviation will magnify over time exponentially.

As far as I know, the 'original' F/A-18 (A-D) is statically stable. E-F is about neutral or marginally unstable. I wouldn't expect its model depart the trim condition significantly (with no external disturbances) in less than 7-10 seconds...

@JZYL, As you said the value of 1e-10 is well within the trim error, should I round off? Because Matlab is not considering it zero and it grows with time.

@Zeus, As you have stated, velocity is constant for the first 45 sec.

Computers in these days do not care about "significant decimal digits" for computation as they use binary IEEE-754 representation internally. The typical number sizes are float (most often 32 bits in these days) and double (most often 64 bit). C offers 80-bit extended precision (long double) and sometimes 128 bit double is available. You can read about sizes here. In addition, some programming languages and packages can do arbitrary precision but it is usually slow.
There are often "corner cases" in model that may require unusually high precision. For instance, the expression (a-b)/(c-d) may be very tough to compute when a gets close to b while c gets close to d. Because of such cases, I usually prefer to use the highest precision available (least long double) in simulations. It may even be corner cases that require complex type arithmetic, even if both input and result are of the real type (sqrt(-1)**2).
Smaller sizes are often not even faster. They sometimes make sense if you work with data matrices so large that memory becomes a problem, of if you use a gamer GPU card for computing that does not feature double precision.
For human readable reports, it is common to leave enough decimal digits to represent the value with known accuracy, or one more, but not longer. For instance, if the value is known with the 0.1 accuracy, it could be printed as 0.6 or 0.66 for instance, but not as 0.6666666666666666. But if this text output is not for humans and will be read back by computer, there is no reason to limit the number of digits. Also, if you know more digits, rounding can only do the same or worse.

This is all hardly relevant for the question, but I can't help but nitpick that 80-bit precision is a feature of the Intel FPU (and some others), rather than that of C. In fact, C doesn't guarantee much in this regard; specifically, in Visual C long double is 64 bit, whereas in gcc it's 80 on the same hardware.


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Are there any safety or technical reason airlines do not display flight information to passengers in real-time?
A newer addition to commercial airliners is seatback screens, that allow the passengers to watch movies, TV, and so forth. On most airlines, there is also a map, that shows you the aircraft's flight path, position, airspeed, and altitude.
I have noticed that the information displayed on the map screen only updates in roughly 15-second intervals. Is there any reason for this? I can't imagine that there would be any bandwidth limitation issue for such a small amount of text data (for example, I can drive a ton of data to my ForeFlight app with my relatively mid-range GA IFD), so I imagine there must be a safety or technical reason for it.

Is it possible to zoom in on that map?  If not, how many pixels would the icon move in 15 seconds?

In 15s, the aircraft moves by 2 statute miles

@DanPichelman With JetBlue, it swapped between three various views - looked like a "US View", to a 500-mile view, to a 250-mile view. Just estimates of course. The map is secondary, I'm more interested in why altitude and speed only update every 15 seconds, as that is simple data.

It's possible that the source of the data is only updated every 15 seconds

Do most people really care? If there's no demand (and thus, requirement) for it, the 15~s interval may simply be an arbitrary software value on the airline or OEM's part that seems "about right." They could have simply decided on 2, 5 or 31s and it wouldn't have made any difference. (Okay, maybe 31s is a bit long.)

@aerobot As a pilot, it mattered to me. It also mattered to the other 8 pilots I was traveling with. It's not "needed" information, but it goes along the lines of, why do they give us fre snacks? We're not going to starve inflight, but it's still nice to have. Same applies to the information - it's nice information to know.

@selectstriker2 I imagine the aircraft's own air data computer should be updating much faster than that, so perhaps it is the entertainment system's computer that updates itself from the air data computer at a much lower rate.

I haven't designed IFE systems, but as I understand it there is an air gap between the cockpit instruments and the IFE, so they wouldn't be the source of this data. I'd expect something like a standalone GPS system for the IFE system.

@selectstriker2 TIL. Why the air gap, is the question that now comes to mind. Also sounds like you're on to the beginnings of an answer =)

@selectstriker2 They transmit data wirelessly though. For example, I can monitor data on my IFD through ForeFlight, and it updates in realtime.

What possible reason is there for a passenger to see updates more frequently than that? The first question of an aviation system designer is going to be "why should we do this" rather than "why should we not do this".

@Matt there is a difference between providing additional information to the pilot through an app like ForeFlight and providing information to the general public sitting in the cheap seats.

@aerobot the reason for the air gap is that one part of the system went through a rigorous (aka expensive) certification process for installation in the aircraft (avionics) and the other system (IFE) does not go through the same process (if any).

@DJClayworth So you're saying there must be a positive reason for doing anything? Fine. By your own argument, the aviation systems designer must have had a definite reason for choosing the update frequency they did. This question is asking what that reason is.

@selectstriker2, IFE absolutely goes through a rigorous certification process.  https://www.swissinfo.ch/eng/electrical-fire-downed-swissair-flight-111/3238752

@MichaelHall true, the IFE system may go through electrical and environmental testing (DO-160) along with the TC/STC work. My point is that the IFE software likely hasn't been through DO-178 and would probably air gapped from the avionics

@selectstriker2, I can tell you that our stuff absolutely went through DO-178 and 254.  Anything going on a plane needs appropriate rigor, the difference is in the DAL.

That's good to know. Are IFE systems treated as DAL D or something higher?

If data is continually updated, nervous flyers will fixate on every minor change.

The altitude changed by 30 ft in one second?That is a descent rate of 1,800 FPM!  Surely we're going to crash!
The speed changed from 480kts to 470kts in one second?At this rate, we will stall in less than a minute!
The plane was at 260kts at 9,800ft?
This crazy pilot is breaking FAA regulations and must be reported!

By updating less frequently, there is a natural filtering and smoothing of the data to obscure tiny measurement changes due to instrument limitations or conditions like turbulence.

Definitely possible. Do you have any source to back it up though?

also it becomes boring too quickly

260 at 9800 on the IFE is no problem at all though - the IFE normally only gives ground speed, not indicated :)

@CptReynolds yes, but it wouldn't stop some pax with too little knowledge from complaining!

@abelenky I was only nitpicking :) of course! Although actually the (relatively few) people I know who don’t get ground vs. indicated wouldn’t have any clue about 250 below 10.

@Matt I don't know if the channel 9 live ATC provided by some US airlines still exists, but there are plenty of stories of pax listening in and making complaints when they think the pilot did something wrong. This would be the same, there doesn't need to be a paper to confirm that.

Actually, I've never seen a flight system that reports KIAS to the passengers. They always report ground speed (usually in kmph or mph), head / tail component of winds aloft, altitude and outside air temperature. One has to do some math to work out the KIAS.

Nervous fliers don't need flight information to be nervous.  They do not even need to get on the plane.

In flight entertainment systems are designed to be cheap, not good.  Most things in them do not work very well; there is nothing special about the flight information updates.
Most passengers want to watch movies, so that's where the effort is concentrated.

I think the same people who design inflight systems must also design car infotainment systems. Neither work very well, nothing special about either of them.


text:
Could the filming of the 747 in "Awakenings" have taken place during the 747 flight testing?
In the 1990 film "Awakenings", the main character Leonard awakens after suffering from a catatonic illness for 30 years.
There's a scene where Leonard watches a 747 landing in New York at JFK. This is considered to be an anachronism/continuity error in the film, as the film takes place in the summer of 1969 and the 747 didn't enter revenue service with Pan Am until early 1970.
However, I know that the prototype 747 first flew in late 1968, and my guess is that by the summer of 1969 several aircraft had been produced, and flight testing was ongoing.
My question is if there's any 'plausibly deniable' way Leonard, in the world of this "based on a true story" yet finally fictional movie, could have actually spotted a non-revenue service test flight 747 landing at JFK in the summer of 1969?

I'm more wondering along the lines of if I were transported back in time to the summer of 1969 and hung around JFK, did pre-revenue 747s ever land there? Or did all testing prior to its introduction with Pan Am occur in controlled environments where it wouldn't be observable by the public?

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text:
What are the drug testing procedures for EU airlines?
How do EU airlines test aircrew for drug use, specifically marijuana? Do they use hair tests, and how far back in time can they detect marijuana use?

Maybe you can simplify your question, which boils down to "Are drug tests used by the EU airlines  able to detect I smoked one cigarette of marijuana 3 months ago".

@mins Well, there's "are they able to?" and there's the implicit "is it necessarily going to be a problem?". (I don't know the extent to which the latter is relevant; it may well be very relevant, or the OP might be able to show that this really was a one-off incident and it might not be a showstopper.)

@michael-kjörling I would say I drink less than an average person, maybe drinking more than one beer only once every three weeks, it was  a special occasion.

what im looking for here is someone who has any experience with getting hired in the EU, and who could let me know what kind of testing is regularly used, as I have no contacts in the industry....

"I have never been a drug user in my life, I smoked marijuana" - You don't show any awareness of the contradiction here. Particularly in context

@RedGrittyBrick I am aware of it, what I meant by drug user is someone who uses drugs with any regularity, which is of course not my case. I am aware of the illegality of the subject, I was not in personal possession of any of it, and never have been.

I am not a pilot but you may find the following useful:
Civil Aviation Authority, INFORMATION NOTICE, Number: IN–2015/012

5 Drug and Alcohol Screening Programme
5.1 The  testing  process.
Trained  staff  should  carry  out  screening  tests  usually  by  mouth  swab,  breath,  blood,  hair   or  urine  sample.  Tests  are  becoming  simpler  to  administer  and  less  invasive  as  the  technology  continues  to  improve.  Minimal  notice  should  be  given  of  the  intention  to  undertake  random  testing.  The  sample  collection  and  testing  process  should  be  designed  to  ensure  the  result  is  reliable.  If  a  positive  result  is  found  further  (usually  blood)  testing should be undertaken. A confirmed positive result should be reported to the relevant Civil Aviation Authority regulatory authority; in the UK the report should be sent to the Medical Department of  UK CAA  for aviation licence holders.

It is easy to find companies whose business is testing UK pilots for drugs, for example AlphaBioLabs:

Protecting the aviation industry with drug and alcohol testing
We specialise in providing drug and alcohol testing to the aviation industry for both individuals who want to show that they are drug or alcohol-free and companies as part of their drug and alcohol testing policy.
Our aviation industry workplace testing consists of the following:

Random drug and alcohol testing
Pre-employment drug and alcohol screening
For-cause drug and alcohol screening
Post-incident drug and alcohol testing
Abstinence monitoring

We have a team of fully trained sample collectors in your area, ready to collect your drug and/or alcohol samples from your place of work or any safe environment.

...

Hair drug testing
Hair drug testing is a form of workplace drug testing that can be used to support other methods such as oral fluid and urine testing.
It can be particularly useful for a more comprehensive overview of a person’s drug use as it is known as a ‘wide-window’ form of testing, which can determine a history of drug intake for up to 12 months.

A different lab reports

British Airways, for example, tests urine for drugs and breath for alcohol. Workers can be randomly tested in the first six months of employment or if returning to work after rehabilitation, and can also be tested if it is suspected that drugs or alcohol may have caused an accident, or if they are suspected of being under the influence while working.

Relevant incidents might include things like this:

Air Astana, which is part-owned by UK firm BAE Systems, said it fired the pilot immediately and had a zero tolerance policy for drugs and alcohol.
In a statement to Reuters it said: “The airline regularly tests its crews for alcohol and drugs using a random sampling method."

I'm not a pilot, but I'm a drug testing lab engineer and can provide some info. There is the EU airline drug testing for aircrews is conducted in accordance with the EASA’s regulations.
On 24 March 2015, a tragic accident sparked the adoption of Commission Regulation (EU) 2018/1042 by the European Commission. This regulation requires alcohol and other psychoactive substances testing for flight crew and cabin crew members on aircraft using aerodromes in Member States - an obligation that has been applicable since 14 February 2021.
Pre-employment, random, reasonable suspicion, and post-accident tests are all required by the EASA to ensure safety while flying. The most common form of drug test used is urine testing. However, hair tests can be performed too but only on occasion. Hair testing can detect marijuana use up to 90 days after consumption, that is why it is used only if it is needed to check a pilot for long-term drug consumption. There is provided pilot drug testing at Claritas Genomics, if you want to know what you might be up to, the up-to-date article can come in handy.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

the name of the company does not sounds related to drug testing, and the company allegedly closed down 5 years ago (https://www.insideprecisionmedicine.com/news-and-features/claritas-genomics-ceases-operations-five-years-after-spinout/) I don't see how this answer is relevant

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What do I need to do to fly a Microlight to France?
I wish to fly a C42 to France from the UK. I can file the flight plan from Skydemon, but I have an NPPL, so I believe I need to obtain permission from French authorities and maybe do other things.
Please could someone tell me what to do and ideally provide links to any online forms etc.
many thanks

Suspect all the info is here: https://www.bmaa.org/flying-abroad

Going the other direction, I read somewhere that Bleriot wasn't allowed to disembark until a British official clambered aboard and declared that his contraption wasn't a plague ship.


text:
Can passenger airliners hover completely motionless in the air?
I've seen many stories of this occuring on r/glitch_in_the_matrix (a popular Reddit). People have been seeing big airliners just paused in the air, not moving. Some of them stopped their car and saw that the planes still weren't moving. I thought an airplane would stall if it went too slowly? I'm not a plane expert but can newer passenger planes hover in the air?
Edit - often times, the planes are not high up, but coming in to land or take off. Someone said they were watching planes take off or land, and suddenly a big jet just paused in mid air for 30 seconds before starting to move again.

Related: If the speed of wind at ground is 200 kn, could an Airliner land vertically if it's course is opposite to the wind's direction?

also note that bigger aircraft seems to move slower, and if the background (clouds) also move, it may be hard to figure out the motion of an aircraft.

The moral here is: don't believe everything you read on the Internet.

@CatchAsCatchCan: Indeed, don't even believe everything you think you see.  Look up optical illusions for examples.

Video or it didn't happen.

Well, the An-2 has been used as a short-haul airliner (and it probably still is, in remote locations), and it can hover even in a slight breeze, but I doubt this question is about anything smaller than a Fokker 70.

@LawnmowerMan Here you go. https://www.youtube.com/watch?v=82JuAcyN5kk

Notice that in videos where the airplane appears to be hoovering the angle is carefully chosen (from behind). If it were to be filmed from the side, it would look different.

@BrianDrummond Well played, sir!

It's called vection? https://en.wikipedia.org/wiki/Sensory_illusions_in_aviation#Vection I was googling the reverse of Peripheral drift illusion and lo and behold it's about aviation.

Yes, but it is only perceivable by people who have taken the red pill. (/Joke alert)

@LawnmowerMan - video and clear evidence the video isn't photoshopped or it didn't happen.

For information only: In WW2 in the Western Desert Germans reported that the British were using helicopters. They weren't. It's believed that they may have seen a Fairey Swordfish going upwind, or trying to :-).

In theory they can stop moving relative to someone standing on the ground. In practice this does not occur.
Aircraft fly through the air and, yes, below a certain airspeed, an aircraft will stall. Let's take a super-simple example to explain the situation:
You are standing on the ground on a very breezy day. It's quite windy on the ground, and blowing even harder at altitude. For the sake of this example, let's say at 15,000 ft. There is a 150Kts wind from the west. A small airliner is slated to go west at 15,000 ft and levels off but slows down to a cruise speed of 150Kts. The airplane is still moving through the air at 150 Kts, but the air is moving in the opposite direction at the same speed. In terms of a fixed point on the ground the airplane does not move.
However, big jets are capable of flying faster than even the biggest practical headwinds. You can, however, observe this in small aircraft on a gusty day (I have flown a PA-28 backwards in this scenario). Here is a video of someone doing it in a slow plane.
What is likely occurring is that a plane that is very high up and very far away appears not to be moving due to its small size in the sky and lack of surrounding points of reference.

Not only are jets capable of flying much faster, they are not capable of flying this slow. 200 KTAS at FL300 is about 125 KIAS, well below clean stall speed of most airliners!

@JanHudec my mistake i will correct to better reflect it was mostly a simple case i was trying to lay out.

in your example the wind and the plane are moving at the same direction, are they not? easterly wind (from the east) vs plane going west (from the east)

… the thing is that there are no 300 knot winds. The jet-streams look pretty strong today at FL300, but they top around 150 knots, and it's not much different at FL400. They occasionally reach 200 knots, but 300 knots is stretching it too much. And that's still ~185 KIAS and if that's even above clean stall speed, it's so far on the back of the power curve that it's horribly inefficient and nobody's going to fly that slow.

Is there not a direct opposite meaning to "an east wind", and "an easterly wind"? In my classes on vector addition, I always used "from the east" for clarity...

Ive added some hopefully more realistic wind speeds and altitudes

@DJohnM no, all three mean the same.

It's a cheap (well, inexpensive) thrill on a windy winter day in a 152.  Low cold-air stall speed plus strong headwind, and you're flying backward!

@DJohnM At least in the U.S. "East wind" and "Easterly wind" both mean "the wind is coming from the East."

Unequivocally: no. Big airliners (or passenger planes of any size for that matter) do not hover in air.
From a moving car, train or such it is possible to have an illusion that an airplane hovers midair, but someone who was claiming that they were standing still and witnessing an airliner hover in the air, was most probably deceived by one's senses. It might also be that the motivation for such a statement is the sheer joy of trolling, or, in extreme cases, pathological need to make things up, or hallusinations induced by drugs and/or mental disorders.
The bigger the plane, the slower it seems to move through the air due to our brains' limited capability to compute the size and speed correctly. This is a contributing factor when observing big planes from moving vehicles and misjudging the planes to be still. Also a layer of cloud at a proper distance with right direction and speed of motion will create an illusion of the plane floating in it's place.

The aspect also matters. When you observe aircraft flying directly towards you, the change in size is slow enough that it is imperceptible and the aircraft may look standing still.

+1 for your general point, but “either lying or hallucinating” is a bit strong: most likely they are just being deceived by a simple optical illusion.  But what they definitely are is mistaken, for one reason or another.

Fair enough, I'll admit to my mistake and edit the answer to be more appropriate
@PeterLeFanuLumsdaine

@Jpe61 I've seen a few instances like this around: https://www.youtube.com/watch?v=IPOtDPHjW-Y. I don't know if the world has ever seen wind speeds high enough to make the same happen to, say, an A318, and I agree that the proposition that airliners "suddenly" stop in the air while coming in to land is preposterous, but where precisely is the line that says A318 (unequivocally) can't do this (given exceptional headwind) while this smaller plane can?

Given the sources the OP is looking at, lying is a very real possibility.  Removing that entirely from your answer wasn't a good idea.  I assume people intentionally troll reddit's /r/glitch_in_the_matrix by simply making up fake accounts of seeing things (lying), as well as wishful thinking helping people's senses deceive them.  Or not exactly troll reasons for lying include making yourself important (i.e. quackery).

You are correct, but I think best to give everyone a benefit of doubt when comes to motives...

Sure, I'm not saying everyone is intentionally lying, but promoting skepticism of claims on the Internet is certainly a relevant part of an answer to this question.
There are quacks and trolls that know they didn't see anything, but want you to think that.  (And probably many more people that think they did see something.)

@PeterCordes I put trolling and such back into the answer with a bit more careful wording. Might as well keep this one rolling as the more serious answers seem not to gather much interest ;)

A plane requires air moving over the wings to generate lift. If there is no air movement, there is no lift, and the plane will fall. Note that this requires that the plane is moving relative to the air, but not necessarily relative to the ground. In theory, you could have a plane pointed into a very strong wind that would have an airspeed sufficient to generate lift, while having a groundspeed of 0. In practice, you'd require a constant ~50mph wind to generate enough lift to keep even a small Cessna aloft. The stall speed of commercial airliners is over 100mph, so you'd have to be flying into the upper categories of hurricane-force winds to have airspeed sufficient for flight while maintaining zero groundspeed. So no, passenger airlines do not hover - in any realistic circumstance, a plane in flight is always moving relative to the ground.

If a jet airliner "suddenly just paused in mid air for 30 seconds before starting to move again," a hundred passengers would be furiously tweeting about it.  We'd also likely have video of coffee sloshing over everything in the cabin and similar unpleasantries, resulting in an FAA Incident Report.
The lack of such on-board complaints of sudden braking and accelerating casts doubt on any reports of the same made from terra firma.

I think the name of the source the OP cited (reddit r/glitch_in_the_matrix) comes with an inbuilt explanation for that: time would also pause for the airliner and its internal volume.  (Yet somehow it can still reflect photons, I guess giving extra proof that such an event could only be explained by out world being an imperfect simulation.)

This is a case where there are caveats on caveats.
No. The standard meaning of "airliner" refers to aircraft that require airspeed to produce lift.
Except yes, airspeed doesn't have to equal ground speed, so an aircraft can produce lift while having zero ground speed.
Except no, the conditions in which an aircraft would have zero ground speed would generally not apply to everyday life.
Except yes, our perception of motion isn't based on actual speed, but angular speed. An aircraft coming directly towards you or away has no angular speed, and thus will appear to hover. In addition, if the observer is moving and comparing the aircraft's position to a landmark such as a building, the aircraft's angular velocity with respect to the landmark can be zero. And even if the aircraft does have nonzero angular velocity, if it's far away its angular speed can be small enough to be imperceptible.

Any fixed or rotary wing requires airflow to generate lift. Helicopters hover because their rotors are continuously rotating to create airflow. Jet airliners are designed for cruising speeds (true air speed at cruise) on the order of 600 MPH at high altitudes (35,000-40,000 feet or more). They won't fly much slower than that at those altitudes because there is no benefit, and for some aircraft under some conditions, they can't (in the thin air at such altitudes, some fully loaded aircraft with most of their fuel load will be near one of the corners of their flight envelope). The fastest recorded jetstream winds don't come close to that, so would at most slow a jet's progress over the ground somewhat, but never halt it. The slowest a jet airliner will ever fly will be just after takeoff or just before touchdown. In those moments, it will still be flying at a true airspeed of about 150 MPH or more. No aircraft of any type would attempt to take off or land in winds anywhere close to that speed (hurricane force).
Given all that, a jet airliner will never just hang motionless in mid-air, and may only appear to do so because of some form of illusion or mis-perception.

I've seen that myself, in cities.
It's an optical illusion
To the novice, most jetliners have the same basic shape (planform).  Embraer, SuperJet 100, B737, B767, B777, A380, Me262.  All the same shape but dramatically different sizes.  But, fairly comparable approach speeds, for traffic control reasons.
And they are far enough away that people trust their view of shape more than their stereovision.  So they are relying on the visible size of the airplane to judge its range.
And so, the Embraer seems to zip across the sky... While the 747 just hangs there if suspended by magic*.  When really, they are both going the same speed, but the 747 is at a much higher altitude.
That will amplify if the person, like many, lives near a regional airport like Newark, Midway, Burbank, Oakland  or National where smaller planes land regularly, but farther from a major international where the big iron are approaching from higher up of course.

A plane flying into a high speed jet-stream head wind could appear stationary from the ground.  But that isn't likely because pilots rarely waste time or fuel.  MORE LIKELY: A jet flying in a line directly toward/away from a viewer may appear not to be moving at all because the change in distance and size isn't obvious at great distances.  The more sinister version is that two airplanes flying flat and level on a collision course appear to the pilots to be stationary - weather they be approaching head on (12 oclock), from behind (6 o'clock) or any intersecting angle in +between.

Ok, review, the answer is NO, but this answer provides good information for readers regarding size and speed illusions that are worth reading.  Please consider the time it took for user46639 to prepare this answer.

authors: Bob Jarvis - Слава Україні


text:
How are Hurricane Hunter planes able to withstand G's as high as 6-7 G in turbulence if the plane is only rated for G loads much lower than that?
I found some conflicting reports on the G limit of the WP-3 Orion, but most sources say the G limit is 2.5 or 3 positive G, which would bring the ultimate load up to 3.7-4.5 G (as there is a 50% safety factor). Similar to the ultimate G loading on today's airliners. The WP-3 Orion is a modernized version of a commercial airliner called the Lockheed Electra. According to the Wikipedia article on the WP-3 Orion, they are not specially strengthened for flying into hurricanes.
There are reports of the WP-3 Orion experiencing G loadings well beyond the ultimate load with little to no damage during turbulence when it penetrated the eyewall, why is this?
https://noaahrd.wordpress.com/2014/09/15/25th-anniversary-of-a-hairy-hop-into-hurricane-hugo/
https://slate.com/technology/2014/08/interview-with-rookie-hurricane-hunter-joseph-patton.html

I am guessing it is because the aircraft are not operating at their max gross weight. Max G loads are for max weights. A lightly loaded aircraft can safely exceed the Max G load.

On top of that are vary large safety factors in the structural calcs, so a structure calculated for the normal load limits may be actually good for 3-4 Gs before anything bends beyond yield.  That plus the bulk of the load being fuel in the wings minimizes the ultimate bending on the wing roots and makes it good for much more.  I know of a CRJ that was subjected to something like nearly 4 Gs negative after a test mishap incident, and the plane wasn't permanently bent and was later delivered to the customer.  What saved it was having an empty cabin at the time.

Possible duplicate of https://aviation.stackexchange.com/questions/43587/is-the-aircraft-used-by-noaa-specially-modified

@JuanJimenez, not a duplicate; that Q/A does not seem to discuss G loading anywhere.

@JanHudec That Q/A addresses the same core question posed here, why the aircraft is so sturdy.


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Modern airliners are designed to be able to withstand the worst (vertical) turbulence. But what about the rarer lateral (horizontal) turbulence?
'Extreme' turbulence is a derived vertical gust velocity of >3,000 fpm (50 fps) that causes a vertical G-load of >3. The limit turbulence intensity for a modern day airliner is 90 fps. (there is likely a 50% safety factor, so the plane is capable of withstanding more).
Lateral turbulence is the type that puts most stress on things like engine pylons and the vertical tail, rather than the wings. An accident involving lateral turbulence is BOAC Flight 911 and the B-52 crashes (Savage Mountain and Elephant Mountain).

The only thing I can think of that would impose extreme lateral gusts like that would be, maybe, wake turbulence from really big airliner hitting a smaller one behind it, or maybe hitting some kind of rotor just so.  Maybe running into mountain wave rotor while parallel to the wave?  Or CAT on the boundary of a jet?  The risk of breaking the fin off from excessive rudder use is the bigger problem, like what happened to that Airbus that crashed into NYC just after 9-11 from rudder overcontrolling by the pilot.

@PeterKämpf do you mean lateral or vertical are more dangerous? There appears to be a typo at the end of your sentence.

The lateral lift curve slope (better: Sideforce slope) is much lower than the vertical one. A lateral gust that does damage needs to be much stronger than an equivalent vertical one.

Hi Lars, thank you for pointing out my mistake. I deleted the comment and replaced it with a hopefully better one.

Yes they are.  FAR 25.427 has the requirements for lateral gust loads.
I don't know if there was FDR information for the BOAC flight, but it may very well have been a similar event to AA Flight 587, the one that lost its vertical fin over NYC when the pilot got on the pedals in reaction to a wake turbulence encounter that induced a large yaw, and made rudder input loads that the fin is not designed to handle.
In that case the fin broke off not because of the gust, but because of the control response.  You will likely be out of phase in the attempt, and your inputs become "doublets"; amplifying inputs that make the yawing worse.  You don't normally touch the rudder pedals on an airliner between departure and landing unless an engine quits; you just let the yaw damper take care of yaw excursions like that and it'll have no problem staying in phase to dampen the motion.  I'll bet that the BOAC incident was that sort of case, where a gust reaction was followed by an input, at high speed.

Thanks for that. I'm a little rusty, but what gust strength (in fps or mph) would be required to cause the vertical stabilizer to snap off, like in BOAC 911? I remember reading about the accident saying they estimated the gust strength to be 140 miles per hour, hitting the vertical tail broadside.

I have no idea what the numbers are. Peter might know, or know where to find it.  I added some extra context to my answer.

A gust would be unlikely to snap the tail, because the gust is pushing on the fuselage as well as the tail. The problem in cases like AA587 is that the first rudder input had everything moving in one direction, then the next input pushed the tail hard in the opposite direction. Normally, having the rudder push the tail simply moves the rest of the plane with it, but in that case the momentum and the forces involved got out of hand.  A gust pushing on the whole aircraft together would have neither the effects of momentum nor the push-on-the-tail-only that broke the American Airbus that day.

I just described exactly that in my answer.  That's what a "doublet" is.  When testing the yaw damper system during production test, you disconnect the YDs and perform a very mild doublet on the pedals to get a dutch roll going, then reengage a YD channel.  You do not try to correct any yaw excursions on a swept wing jet by trying to counteract with rudder.  You will be out of phase and just get a dutch roll PIO going.

FDR information was not available for BOAC 911.  (The aircraft had an FDR, but it was destroyed by the postcrash fire.)


text:
What is a tailwheel aircraft?
I just had a lesson in a SGS 2-33A and my CFI logged it as tailwheel time "because it has a tailwheel".  I laughed and said I'm not sure that's how it works.
The center of gravity is in front of the monowheel and SOP is to wheel land it on the monowheel and then go forward onto the skid.  I wouldn't have thought it counted as tailwheel because the CoG is in front of the monowheel, making it dynamically stable.
What is the official definition of a tailwheel aircraft, and is there anything to stop me from logging this time as tailwheel time?
The closest I could find was PHAK 3-7 "Landing gear with a rear mounted wheel is called conventional landing gear."  But is there anywhere to find the definition in 14 CFR?
Under the PHAK definition, if you mount a vestigial tailwheel on the rear of a tricycle-gear experimental aircraft, it would be considered to have conventional landing gear.  What's more, you would be able to fly the experimental aircraft solo without a TWE to build TW time.

It is wrong because "tailwheel" is only a slang term for conventional gear, and the type of gear is not determined by the existence of a wheel on the tail but rather as you described the center of mass relative to the main gear when in the flight configuration(with pilot and such).
Conventional gear may use a tail skid or ski rather than a tail wheel, and the tricycle gear planes that I fly have a tail skid to protect the frame from excessively nose-high takeoffs and landings but this does not make them conventional gear.


text:
What determines the touchdown zone and aiming point markings on a runway?
Large runways usually have a marked touchdown zone, and a marked aiming point (with two giant bars in the US). How is that location chosen? It seems like it is frequently further down the runway than I would have thought maximized available runway length.
How important is it for an airliner to land on that spot? Are there regulations about this?

this page seems relevant: http://code7700.com/aim_point_vs_touchdown_point.html

I think that page answers your question. Make yourself a nice summary from there, link it, and self-answer!

There are actually several different indicators on the end of a runway. Here's a diagram of the most common ones during the day:

... and at night:

The first touchdown indicator, as shown, is usually placed a set distance (here 500') from the threshold of the usable runway. Then, there are additional markers at 500' increments. Which one the pilot will aim for on approach depends on the plane he's flying, its weight, and instructions from the tower such as to land "deep" or "shallow" (light craft, and sometimes even commercial airliners, are often given these instructions to help manage air and ground traffic more efficiently at peak times).
As you can also see from the night shot, the glide slope lights (here using a system called PAPI which is a more precise indicator of slope than the older and more well-known "white-over-red" VASI) are positioned smack in the middle of the touchdown zone; again, with an approach path aiming directly for that point from the pilot's perspective, the plane will touch down on full-strength runway pavement even if he's in a 747-800.
Of course, maintaining that glide slope all the way in is not the greatest idea, as a standard descent rate for an airliner on final approach is 400ft/min, which works out to more than 6 feet per second. Even the cushiest main gear struts are going to make that a pretty rough "smack" in the seats of the passengers and can cause very expensive damage to the airframe itself. To avoid that, pilots usually add a little throttle and/or pitch up a few more degrees in a maneuver called a "flare", which reduces the rate of descent, ideally zeroing the plane's descent rate just as the wheels touch. This means that during the last few seconds of approach, the glide slope decreases, moving the "aim point" further up the runway and causing the main gear to touch further down the runway.
You'll find that if you look at the touchdown marks on older, well-used runway surfaces, touchdown of the main gear (remember that's anywhere from 50 to 150' behind the pilot's perspective and up to 25' below it) actually ends up centered pretty close to the ideal spot, due to the leveling off of the flare maneuver:

You can see in this image the average touchdown point (the widest and blackest part of the runway) is right at the PAPI lights to the left.
You'll also notice a few significant tire marks just a little too close to the threshold for comfort. Clearly landing a plane is not an exact science, and this is why the touchdown zone and aiming point is further down the runway than you might think; a sudden downdraft or a thinning of the air due to surface heat at just the wrong time in these crucial final seconds, and if the pilot was aiming for the threshold, his main gear will touch down short of it, possibly doing millions of dollars of damage to his plane, the runway and approach lighting as well as likely closing the runway.

possibly doing millions of dollars of damage to his plane, the runway and approach lighting as well as likely closing the runway oh, and possibly killing passengers - an activity frowned upon by management.

@FreeMan - That too :-)

Great answer, and I love the squiggly, hand drawn arrows. Perfect!

Throttle is generally cut before the flare, not added.

@fooot - Depends on if you do a pitch flare or an engine flare. A pitch flare is recommended as you say, cutting power and increasing AOA to reduce speed as you touch down, but not always possible depending on aircraft design and conditions. If your AOA on approach is already high (steep glide slope, nose-high approach), pitching further to flare could smack your tail on the ground, or worse, stall you too high to avoid damage and too low to recover. A little extra power will reduce AOA while shallowing the glide slope, the tradeoff being a higher touchdown speed for a longer rollout.

If a standard descent rate for an airliner on final approach is 400ft/min on a standard 3° glidepath, the approach groundspeed would be about 75 Kts. More realistic figures for airliners would be in the range of 500-900 fpm on a 3° gp at 100-160 Kts groundspeed.


text:
Why do some airport towers avoid monitoring 121.5?
In the USA airport facilities directory (AFD), some towers (eg KSJC) are listed with the note:

Emerg frequency 121.5 not avbl at tower.

Why do these facilities not monitor guard? Does the note actually mean that they cannot even talk on 121.5 in an emergency?
I am assuming it is because a different facility in the area (eg a TRACON) is monitoring guard, and they don’t want two facilities taking responsibility for guard. But suppose an airplane is landing in an emergency, does that mean the tower couldn’t even listen to the emergency communications?
How does this work practically in emergencies?

It's hard to imagine being close enough to KSJC that you need to talk to them, yet not being in contact with some ATC facility on a frequency other than 121.5.

121.5 is only used when you don't have anyone specific to speak to or those who do can't help you - for example, having access to primary RADAR. If they direct you to land at an airport, you'll be handed over to the tower as any other approach - probably coordinated via phone between the controllers.

It seems to come down to the point that as long as someone is monitoring 121.5 in a specific airspace then not everyone needs to. And it helps avoid multiple ATC facilities responding to the same call. This is from the FAA's Facility Operation and Administration orders (my emphasis):

3-3-4. EMERGENCY FREQUENCIES 121.5 AND 243.0 MHz
[...]
d. When facilities are in proximity and no derogation of services will
  result, transmit/receive capability should not be provided for each
  facility. The following requirements shall be maintained:

Geographical area coverage shall not be derogated.
DF-equipped facilities shall have transmit/receive capability on 121.5 MHz.
Facilities without emergency frequency capability shall have appropriate landlines for rapid relay of emergency information.

Looking at KSJC, there are a lot of other airports close by, so the potential for confusion or conflict on the frequency seems high. My guess is that they leave 121.5 to NorCal TRACON; KPAO is 10 miles from KSJC and also doesn't have 121.5 available, for example.

I have flown around SJC in a helicopter at 500ft with good radio and radar coverage from Norcal Approach.  The antennas are up on on the surrounding mountains.


text:
Who has authority over stadium TFR exceptions in VFR flight?
I fly in the Bay Area. I sometimes like to fly over SF through the San Francisco Class B. If I am in contact with Norcal Approach and in their airspace, I can ask them for an exception and they can authorize it. But, I could also be talking to the tower, and could also be talking to Oakland Tower.
All three of the following agencies have authority over sections of airspace that overlap with the stadium TFRs at the Giants stadium (see image).

Oakland tower (class C)
San Francisco tower (core class B)
Norcal approach (outside core class B)

My question is: which of these three agencies have the authority to grant me an exception to the stadium TFR?
(Image is SF TAC with TFR plotted by Foreflight.)

The answer will vary based on the location - San Francisco, Los Angeles, and New York may each have different arrangements. However, in general, it'll come down to how the different ATC facilities have the situation worked out with each other.
The stadium TFR itself does not help much. The relevant section states that:

THE RESTRICTIONS DESCRIBED ABOVE DO NOT APPLY TO THOSE AIRCRAFT AUTHORIZED BY AND IN CONTACT WITH ATC FOR OPERATIONAL OR SAFETY OF FLIGHT PURPOSES

Any of those facilities could provide the authorization - so it's then down to which will do so. The answer to that will depend on the structure of how the facilities work with each other. The ATC facilities will have Letters of Agreement which state that a given area of airspace is managed by a given facility, as well as how handoffs are handled.
The facility that can provide flight following is also the facility that can authorize you into the TFR in that area. To figure that out, all you have to do is ask: call up Norcal Approach or Oakland Tower, and ask for flight following. If they can do that, then they're the right folks to ask about transiting the TFR. If not, they'll give you another frequency to try. Of course, just because they have authority over the airspace doesn't mean they'll grant the request.

I was in contact with Oakland Tower two days ago during a stadium TFR there, and it's necessary to fly through the TFR there to land at Oakland. When I asked explicitly about it during a loop in the traffic pattern, I was told "just don't fly directly over the stadium".


text:
What is this flyer in a 1911 short film?
In the very first instants of the 1911 comedy short film Robinet aviatore (or Tweedledum Aviator) by Michel Fabre, which can be watched here, on the background some kind of flyer can be seen.

Does someone have a clear idea of what kind of flyer is that? A Wright one?

Given this is an Italian producer and a Spanish director, it could be a European plane, e.g. a Voisin or a Farman, as well.

Given that the short film was produced in Turin (according to the Italian Wikipedia), it is likely that that the Aeroclub of Turin (1908) has more information on this aircraft.
On their website they describe the history of aviation in Turin in the 1909-1915 period(in Italian). Around that time, Turin was a center of aviation in Italy (and it still is).
There were several aircraft manufacturers, including the automobile factory FIAT (Fabbrica Italiana Automobili Torino) which at some point produced Farman aircraft under license.
One of their first employees (employee no.3) was Alessandro Cagno. He was, among other roles, the company's racing team driver. In 1909 he lost interest in car racing and turned to aviation. He became the 10th pilot in Italy, on a Farman aircraft. There are several pictures of him in his Farman III on the internet, which looks very much like the aircraft in the short film.
Below is a picture from 1911 of Cagno in his Farman III in Venice.

By Unknown - over 100 years old. Source: wikipedia
Especially this picture looks very similar to what can be seen in the film, including hills in the background.
More video material of the Farman III can be found here:

You can see that there were several variations on the model.
It may be Cagno's aircraft in the film, or another Farman. Looking at the list of early aviators in Italy, the majority of them got their license in either a Farman or a Bleriot. The latter aircraft looks very different.

Source: Contact! The Story of the Early Aviators, Henry Serrano Villard ISBN: 0-486-42327-1

To me, it seems that the airplane in the movie had two narrow rudders. I have unsuccessfully searched for such a plane (most likely a Farman) myself. I wish I had the 1911 issue of Jane's - at that time it described every single airplane on earth.

@PeterKämpf I think you are right about the Farman. It's probably a Farman III.

I agree. The linked video mixes types - there are some shots of the Farman I as well. But the correct answer is most likely Farman III in one of its many variations.

The aircraft appears to have a single canard forward and two vertical stabilizers aft. Given the likely European origin the closest I could find was the Farman 1 built by the Voisin brothers.

Farman 1

Look at the aspect ratio of the rudders, the unfaired truss holding the canard, the skids in addition to the wheels - no way this was a Farman 1.


text:
Reason why heavy aircraft are allowed to land but not to start
I stumbled upon this article (German)
It says that a few of Lufthansas 747 are grounded at Twente airport. They were parked there because of COVID-19 at an aircraft recycling company.
Now the airport does have the license for such heavy aircraft to land, but not to start, which normally isn't a problem as they land there to be recycled.
Unfortunately the article doesn't state the exact requirements the airport doesn't fulfill. It just says something about safety issues. What could it be that allows the aircraft to land safely but not to start?

What could it be that allows the aircraft to land safely but not to start?

In the USA at least, to allow takeoff, a runway must be long enough to let an airplane reach takeoff speed, decide to abort, and reach a full stop.  That's longer than just landing.
The more ancient answer is: takeoffs are optional, landings are mandatory.  Refusing permission to land would damage Twente's reputation.
Even more ancient, before aviation, a ship in distress would not be forbidden to dock and ordered to head back into the storm.  (Only because COVID is mentioned, ships suspected of carrying plague are a different matter.  See the etymology of "quarantine.")

Greg's answer uncovers the Dutch report, which quotes Meiltje de Groot hoping that the 747's could be scrapped ("ontmanteld") in situ because of lack of demand, because of COVID's reduction of passengers, at Twente because they could land there with no intention of departing.

And even if it wasn't a legal requirement, an aircraft'll still require more runway to take off than to land, because an aircraft'll be carrying more fuel (thus greater weight) and less flap (thus greater speed needed to fly) at the beginning of a flight than at the end, and because aircraft can slow down during landing faster than they can speed up during takeoff.

The article you linked to (and the original one in Dutch from Tubantia) suggest that the problem is a legal one, not a technical or operational one.
There is unlikely to be an actual safety issue in allowing 747 takeoffs. However, the airport does not currently have the correct paperwork to allow that.


text:
Do ANR headsets affect pilots' perception of engine problems?
ANR (Active Noise Reduction) headsets reduce the sound level to a pilot's ears by creating an interference wave that cancels out some of the environmental noise in the cabin. Some say that this reduces the pilot's ability to hear minor changes in the engine's sound, thus delaying the point when the pilot would take action to diagnose the problem or land the aircraft.
Are there any conditions of engine malfunction or suboptimal performance which a pilot wearing an ANR headset would not be able to detect, but one wearing a passive headset would?

Related: Are passive or active headsets preferable in an open cockpit?

In summary, based on FAA/NTSB information it's possible in theory but no one really knows how individual headsets behave and there's no record of ANR headsets contributing to an accident.
First, according to a very short FAA information paper on Noise Attenuation Properties of Noise-Canceling Headsets, it's possible that they can mask important sounds:

While this technology can have many beneficial effects such as
  providing clearer communications, reduced pilot fatigue, and added
  comfort, electronic attenuation of important environmental sounds and
  alarms may occur

But the paper has no specific information or examples, and its only purpose seems to be to encourage operators to do their own testing (which is reasonable, since headsets can be very different):

Evaluations should be conducted while both on the ground and in flight
  during normal operating conditions to ascertain if any audible alarms
  or other environmental sounds, or combinations thereof, can be
  detected while electronic noise attenuation is on and active.

That paper is from 2007 and a letter of interpretation from the same year on headset requirements in part 121 operations implies that the FAA's main concern with ANR headsets is (or was) that the batteries run out and that might cause problems:

The FAA is particularly concerned, however, that Active Noise
  Reduction (ANR) headsets and headset adapters [...] that rely on
  battery power are subject to failure when [...] batteries discharge
  under normal use

And the FAA's general brochure on Hearing and Noise in Aviation mentions ANR headsets without any warnings or recommendations.
Finally, the NTSB's accident database has only one specific reference to an ANR headset (that I could find) and it explicitly ruled out any effect:

On January 5, 1998, the NTSB IIC used a Cessna 208B to determine if
  the Telex model ANR-4100 active noise reduction headset worn by the
  pilot at the time of the accident could have eliminated his ability to
  hear stall or fuel selector warning horns. All aural warnings were
  clearly audible with the engine operating and the headset active.

The information I found online on ANR headsets is overwhelmingly positive and I couldn't find any informal reports of pilots mishearing engine sounds either.

well researched! Most 121 jet operators use single-ear headsets

Although its possible to detect engine problems audibly, I don't think that's the primary mechanism (except for engine out) by which pilots are expected to detect engine anomalies. Part 91.205 requires that every aircraft be equipped with the following instrumentation, and these should be the primary mechanism by which engine malfunctions are detected.

(4) Tachometer for each engine.
(5) Oil pressure gauge for each engine using pressure system.
(6) Temperature gauge for each liquid-cooled engine.
(7) Oil temperature gauge for each air-cooled engine.
(8) Manifold pressure gauge for each altitude engine.
(9) Fuel gauge indicating the quantity of fuel in each tank.

That being said, ANR headsets attenuate sound, but don't eliminate it entirely. Having flown with an ANR headset for most of my flying career, I can certainly hear variations in engine noise in the mag check and prop exercise during the runup, as well as during throttle and prop changes. I can also hear a fouled plug during runup, as well as verifying it visually on the gauges.

When talking about GA, if (for example) one spark plug goes bad, you can actually notice a difference when listening closely, and i doubt you could hear that with ANR! But one spark plug that goes bad during flight is not gonna kill you (well, hopefully anyways!). If there is a problem that will cause major power loss on the engine, you will definitely hear it! Other things like engine roughness, which is primarily as sign for lack of carburetor heat might not be heard though. Yet, when flying with a normal headset I find it hard to hear when the engines sound changes over some time anyways.
A ANR headset will reduce, but not limit your ability to hear the engine. It is a lot more comfortable during cruise though.

I can certainly hear a fouled plug during run-up with an ANR headset. it may be because of the 250RPM drop in my airplane. if you are fouling plugs in flight, you need to lean

Yeah, during run up they are easy to identify, not only do you see and feel it whenever you go to a single magneto but you can clearly hear it as well. When this happens in the air though (happened twice to me already^^), it might be really hard with ANR as it is already hard with normal headsets.


text:
What protection does Vno provide?
VNO, the airspeed where the green and yellow arcs meet on the airspeed indicator, is the "maximum structural cruising speed" (FAR 1.2). An airplane should only be flown above VNO in calm air. Comparing this to VA, the speed below which the airplane will stall before reaching its load limit, what protection does VNO provide? Turbulence that mimics a full deflection of a control surface would likely qualify as extreme, but what's the middle ground?
VA varies by airplane weight. Does VNO vary by weight, and is the calculation the same?

In short, VNO doesn't provide you any protection, it just tells you that flying that fast puts you in a regime where structural damage will occur before increased load factor will cause a stall -- regardless of weight.
For part 23 airplanes that are not turbine powered and VD has not been established, 23.1505(b) establishes VNO must be established such that it is between VC,min and 0.89*VNE.  Section 23.335 defines VC as a multiplying factor of the square root of wing loading at design maximum takeoff weight.  For normal and utility category airplanes, VC is design cruising speed and is be between 33 √(W/S) and 0.9 VH where W/S is wing loading at the design maximum takeoff weight.  The factor 33 may be scaled as low as 28.6 based on W/S values greater than 20 (the regs do not provide units on any of these numbers...).   VH is the maximum forward airpseed in level flight at maximum continuous power at sea level.
Section 23.335 also defines VA and the only relation to VC is that VA need not exceed VC.
We can see from this information that establishing VNO is a design choice based ultimately upon maximum possible wing loading as a guideline and unlike VA stall speeds are not involved in the calculation.
What you can take from this is that VA will vary by weight (because this affects the stall speed) but VNO is based upon wing loading at max gross takeoff weight and is constant with actual weight.
Flying slower than VA you will stall before causing structural damage.  Flying faster than VA you will cause structural damage before stalling the airplane.  VNO will be at least the VA or higher.  Flying below this speed doesn't really tell us anything (VA is better for that), but flying above this speed lets us know the design margins for load factor induced structural damage are such that we don't want bumps or abrupt control deflections because we can damage the airplane.

Regulation excerpts.

§23.1505   Airspeed limitations.
(b) The maximum structural cruising speed VNO must be established so that it is—
(1) Not less than the minimum value of VC allowed under §23.335; and
(2) Not more than the lesser of—
(i) VC established under §23.335; or
(ii) 0.89 VNE established under paragraph (a) of this section.
(c)(1) Paragraphs (a) and (b) of this section do not apply to turbine airplanes or to airplanes for which a design diving speed VD/MD is established under §23.335(b)(4). For those airplanes, a maximum operating limit speed (VMO/MMO airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations.

§23.335   Design airspeeds.
  Except as provided in paragraph (a)(4) of this section, the selected design airspeeds are equivalent airspeeds (EAS).
(a) Design cruising speed, VC. For VC the following apply:
(1) Where W/S′=wing loading at the design maximum takeoff weight, Vc (in knots) may not be less than—
(i) 33 √(W/S) (for normal, utility, and commuter category airplanes);
(ii) 36 √(W/S) (for acrobatic category airplanes).
(2) For values of W/S more than 20, the multiplying factors may be decreased linearly with W/S to a value of 28.6 where W/S=100.
(3) VC need not be more than 0.9 VH at sea level.
(c) Design maneuvering speed VA. For VA, the following applies:
(1) VA may not be less than VS√n where—
(i) VS is a computed stalling speed with flaps retracted at the design weight, normally based on the maximum airplane normal force coefficients, CNA; and
(ii) n is the limit maneuvering load factor used in design
(2) The value of VA need not exceed the value of VC used in design.


text:
What qualifies a UAV as an MAV?
Micro aerial vehicles are a special class of UAVs that have gained a lot of attention and research focus in the past few years. These are generally smaller in size ranging from 3m to 15 cm depending on where you look.
So, is there a clear, recognized or accepted definition of an MAV in terms of size and power? I am interested in the upper limits i.e. the line classifying a UAV as an MAV.

Currently, there seems to be little official definition, and the term MAV appears is relatively new. The only paper on the topic I could find that specifically approached the area defined it as:

"small enough to be practical for a single-person transport and use." (Galiński and
  R. Żbikowski, 2007)

Delft University of Technology section on MAV research provide no clear definition in their documents.
I think the definition seems to more subjective to the flying properties to the UAV, which might make the definition more difficult. Since they are not carrying people but sensors, they will be much more varying in weight, especially in with time.
One example, the british army's MAV has a flight time of 25 minutes.  This one is a very small but has a respectable flight time. This will not simplify definition. I think the term coined by Galiński and Żbikowski is the most useful in a practical sense.
Update:
University of Texas page on the DARPA competion says:

The definition employed in DARPAs program limits these aircraft to a
  size less than 15 centimeters (6 in.) in length, width, or height.
  MAVs must have a weight of 50 grams or less and must be capable of
  staying aloft for 20 to 60 minutes for a distance of 10 kilometers.

The pure source for this this, while not avaliable any longer, I believe I found to be

The definition employed in DARPA's program limits these craft to a
  size less than 15 cm (about 6 inches) in length, width or height. Source

There are currently no civilian classifications for UAVs from the FAA or EASA, hence the legal problem with these. Most army and air force drones operate under military exceptions if I'm not mistaken.

I wouldn't regard some of the large Hexacopters that can be transported and flown by one person as an MAV or even a craft like the Walkera QRx350 or a DJI Phantom; I would call these UAV's.
These Mini and Micro Quadcopters are quadcopters but the MAV term could apply to fixed wing aircraft and helicopters below a certain size


text:
What are the flight rules for crop dusters?
Crop duster aircraft operate much differently than most other aircraft. Are there special rules that apply to their operation? Specifically, are there rules about how close they can fly to structures, terrain, or vehicles?

14 CFR Part 137 regulates agricultural aircraft operations, with §137.51 discussing operation over congested areas, including:

The crop duster must operate “with maximum safety to persons and
  property on the surface” and the crop duster must have obtained prior
  written approval from the FAA and notice of the intended operation
  must be given to the public. Further, the crop duster must submit a
  plan to the FAA that considers the flight obstructions and plans for a
  possible emergency landing.

Of utmost importance is the section regarding the flying of restricted category civil aircraft such as agricultural aircraft:

Sec. 91.313 — Restricted category civil aircraft: Operating limitations.
(a) No person may operate a restricted category civil aircraft— (1)
  For other than the special purpose for which it is certificated; or
(2) In an operation other than one necessary to accomplish the work
  activity directly associated with that special purpose.
...
(e) Except when operating in accordance with the terms and conditions
  of a certificate of waiver or special operating limitations issued by
  the Administrator, no person may operate a restricted category civil
  aircraft within the United States—
(1) Over a densely populated area;
(2) In a congested airway; or
(3) Near a busy airport where passenger transport operations are
  conducted.
...

More information is available in this FAA document.

Thanks for the info. I see the phrases "without creating a hazard" and "with maximum safety". Are there any established guidelines or precedents for these requirements?

@fooot it's a catchall to prevent people dumping highly flammable pesticide over someones barbecue

The FAA issues "Determinations" on a regular basis . These Determinations lay out the guidelines on a number of occasions https://www.faa.gov/air_traffic/publications/atpubs/AIR/air0701.html

hmm, interesting read. Got to wonder how a ferry flight of a crop duster would be allowed under that section, unless that's somehow covered under (a2).

@jwenting "what was that person doing in the passenger seat?" "he was my lookout to make sure I didn't spray campers on my next trip"

@ratchetfreak yeah, but doesn't "(a) No person may operate a restricted category civil aircraft— (1) For other than the special purpose for which it is certificated" preclude a cropduster from being ferried? After all, ferry flights are not "the special purpose for which it is certificated" ;)

@jwenting wouldn't that also mean that flights to a maintenance hanger are precluded?

@ratchetfreak unless that hangar is on the field you're going to anyway at the end of a cropdusting session ;) So maybe you can ferry as long as you dust some crops along the way...

Ag applicators, crop dusters, are generally governed by 14CFR91 for the operation of their aircraft, except when actually performing ag operations, which includes application and travel to and from loads and applications, they are governed by 14CFR137.
Operations over other than congested areas, 14CFR137.49 permits operations below 500 ft AGL, and closer than 500 feet to persons, vessels, vehicles, and structures.
Operations over congested areas, 14CFR137.51 permits wider exceptions to the general rules under 14CFR91, but with various provisions for helicopters, single engine and multi engine airplanes. Additionally, it makes clear that minimum altitude deviations from 14CFR91 are limited to dispensing and approaches and departures for dispensing. It does not relieve the operator from flying at an altitude which provides safety in the event of an emergency, without endangering persons or property on the surface.
Furthermore, 14CFR137.53 establishes requirements for pilot experience and aircraft inspections when ag aircraft are operated over congested areas.
The technology for ag aircraft is changing, and while recip Otto cycle aircooled engines have been employed traditionally, it is much more common to utilize turboprop powerplants. Additionally, turboprop conversions are popular for some traditional ag aircraft. The turboprop enhances reliability substantially, and are equipped with inertial separators to reduce the likelihood of things like the ingestion of birds from causing powerplant failures. Additionally turboprops have enhanced higher altitude performance which traditionally called for the use of more complex turbocharged recip engines or multi engine ag aircraft.
In general, ag pilots have substantial experience, and in general are well versed at low altitude operations. There are some academic and also flight school operations which specialize in training ag pilots.
In short, with appropriate planning, and a good working relationship with the local FAA FSDO office, and appropriate public relations (notice to public required for some operations over congested areas under 14CFR137.51) ag applicators are given wide latitude to perform their function while assuring acceptable levels of public safety.


text:
With the new MOSAIC rule, would it allow for me to operate my Cessna 172 as an LSA and install experimental avionics?
I know it's still early with the FAA’s Modernization of Special Airworthiness Certification (MOSAIC) Notice of Proposed Rulemaking, but as it is currently written (August 2023), could I operate my Cessna 172 as a LSA, and install, as an example, the experimental version of the Garmin G5 ~$1,800 rather than the certificated version ~$2,800, and save myself thousands of dollars?
AOPA's reporting on it makes it seem so:

Among those likely to be enthusiastic about the proposed changes are owners of existing aircraft that could soon qualify as LSAs, and experimental avionics firms that can sell their products much more broadly.

There is no such thing as "experimental" avionics, and very few avionics need any for of certification at all for Part 91 activities. You may install any avionics you wish, so long as the plane's airworthiness is maintained. The broadest way to do that is to get A&P sign-off. However, there are other routes as well. Certified Type Normal gliders all over the US have glide computers, not a one of which AFAIK is certified.

@KennSebesta A big benefit of installing a G5 is removing the vacuum system. I believe the 172's POH lists its vacuum system as required equipment and so needs an STC to remove, which the "certified" G5 provides and the "experimental" G5 does not. No idea if MOSAIC changes any of this or not.

Also if I recall correctly the experimental G5 has some small differences (e.g. the AI can be switched in flight into an HSI and vice-versa) and is not TSO'd. Which I believe would make it illegal for use in IFR flight?

Based on your approximate costs, it looks like a savings of thousand (singular) dollars, not thousands (plural) dollars.

@Chris those are excellent points. It comes down to the motivations for someone to install a G5, and judging from what you say the benefits are definitely there for getting the STC'ed version.

@FreeMan there might also be implications about who does the work. It's generally understood that to get a Garmin device into a TSO'ed panel, multiply its price by two to account for labor, wiring harnesses, etc...If the OP can do some or all of the installation, that alone would save several thousand.

Fair enough, @KennSebesta. I'm a DIYer and work on my house, not an aircraft, so I tend to forget about installation costs.

The short answer is a qualified "maybe."
The heart of MOSAIC is that they're not going to base a 'yes a sport pilot can fly it' rule on aircraft type or equipment package.  They're going to base it on VS1 being 54 KCAS or less (which not all 172s can achieve, so check your specific POH), that it has positive control at virtually all times, and that its controls are characterized as 'simple' or easy to manage (which your experimental Garmin may or may not).
Keep in mind that installing avionics that invalidates it as a non-MOSAIC 172 may mean you (or other operators) lose privileges like the use of seats 3 and 4, or IFR operations, which could also impact resale value.  Make sure you've done your homework and know what the STC could cost before you decide that you're actually saving thousands of dollars.

+1.  This is a great answer.  Cost considerations must include the rules you must abide by, if installed, as the answer states.

No. Under the proposed rulemaking, a sport pilot may act as pilot in command of an aircraft that fits the restrictions (54 KCAS, etc.), but your 172 will still have a standard airworthiness certificate. Per the proposed § 21.181(a)(1):

Standard airworthiness certificates
and special airworthiness certificates
issued for aircraft certificated in the
primary, restricted, or limited category
are effective as long as the maintenance,
preventive maintenance, and alterations
are performed in accordance with parts
43 and 91 of this chapter.

you are still required to perform maintenance in accordance with parts 43 and 91 to keep your airworthiness certificate valid. Per the proposed § 21.190, you can apply for a special airworthiness certificate in the light-sport category if your aircraft meets the requirements of § 22.100. Unfortunately, the 172 does not comply with § 22.100(a)(6):

(6) Not have been previously issued a
standard, primary, restricted, limited, or
provisional airworthiness certificate, or
an equivalent airworthiness certificate
by a foreign civil aviation authority.

and so it is not possible to get a special airworthiness certificate in the light-sport category for a 172.
In short, under the proposed rulemaking, a sport pilot can act as PIC in some non-light-sport aircraft, but this does not make them light-sport aircraft.


text:
In a slip or skid, how does one wing have a higher angle of attack and more lift?
I've discussed this with my instructor numerous times, and I have the concept memorized, but from an aerodynamic point of view, I can't see how the angle of relative wind to chord line is different per wing (assuming a Cessna 172, if that makes much of a difference).
The wings are essentially a straight line over the top of the plane, and relative wind is a single vector - to me, it looks like they should have identical AoAs.
If you know of a graphic or video, I think it would help explain best.

Most, but not all, wings have some dihedral (the 172 does), and I don't think a wing with dihedral (or one with anhedral) can be treated as a straight wing.

@Terry wow you're right; I remember learning that in class a while ago - wonder how I forgot.

You are mostly correct, but the fuselage distorts the airflow in sideslip such that the windward wing sees a higher angle of attack near the root, and the leeward wing a lower angle of attack. Please see the drawing below for an explanation.

The blue lines show the sideward component of air flow and the red arrows the resulting rolling moment.
This is why low wing airplanes need more dihedral, and high wing planes like your 172 almost none. Wing sweep adds more directional stability, and then you even find aircraft with pronounced anhedral, like the Harrier jump jet or the F-104 Starfighter. See this answer for more detail on this.

Thank you! It's still slowly sinking in, but I believe it makes sense :)


text:
Who do I call to pick up my IFR Clearance at KBKL?
I've had my IFR rating for ~2 years now, but haven't done much other than practice approaches to stay current. Flying to KBKL tomorrow, and when I depart to come back, I can't tell who I call to pick up my clearance.
The approach plates say "CLNC DEL 121.9 (when tower closed)" - okay, what about when the tower is open?
I've tried googling around, but the internet is filled with people asking how to pick up clearances in the air; I trained at a non-towered field so I've got the opposite issue.
Thanks!
Edit: Here's a link: http://airnav.com/airport/KBKL

When there is no separate Clearance Delivery frequency, just call on the ground control frequency to get your clearance.
Separate Clearance Delivery frequencies are only needed at busy airports to relieve radio congestion and work load.
Even at a "busy" airport sometimes you will see(hear) one controller work both Ground and Clnc Del when the workload is low.

In this case the frequency is the same regardless of when you use it or who you talk to. Ground-point-nine to talk to Lakefront Ground when they are open, or Cleveland Approach otherwise.

@JWalters precisely. When the tower is open, 121.9 is used by Lakefront Ground (who is also the clearance delivery controller)—there is no clearance delivery frequency when the  tower is open. When the tower is closed, 121.9 is used by Cleveland [Approach] Clearance Delivery—there is no ground controller. Different airports may do it differently, for example at an airport where the tower and approach are closed overnight, clearance delivery might be the overlying ARTCC on the (daytime) approach control frequency.